Raman spectroscopy of uranium compounds and the use of multivariate analysis for visualization and classification

Abstract

Raman spectroscopy was used on 95 samples comprising mainly of uranium ore concentrates as well as some UF4 and UO2 samples, in order to classify uranium compounds for nuclear forensic purposes, for the first time. This technique was selected as it is non-destructive and rapid. The spectra obtained from 9 different classes of chemical compounds were subjected to multivariate data analysis such as principal component analysis (PCA), partial least square-discriminant analysis (PLS-DA) and Fisher Discriminant Analysis (FDA). These classes were ammonium diuranate (ADU), sodium diuranate (SDU), ammonium uranyl carbonate (AUC), uranyl hydroxide (UH), UO2, UO3, UO4, U3O8 and UF4. Unsupervised PCA of full spectra shows fairly good distinction among the classes with some overlaps observed with ADU and UH. These overlaps are also reflected in the poorer specificities determined by PLS-DA. Higher values of sensitivities and specificities of remaining compounds were obtained. Supervised FDA based on reduced dataset of only 40 variables shows similar results to that of PCA but with closer clustering of ADU, UH, SDU, AUC. As a rapid and non-destructive technique, Raman spectroscopy is useful and complements existing techniques in multi-faceted nuclear forensics.

Analysis of Water Coupling in Inelastic Neutron Spectra of Uranyl Fluoride

“…Adding a nearby H-bonded water molecule shifts the frequency bycompared to the measured value of 109.0 meV. This phenomenon has been observed in a variety of other water-containing uranyl species, such as uranyl hydroxide, ammonium diuranate, ammonium uranyl carbonate, sodium diuranate, and uranyl acetate 45–47 . This mechanism of H-bonding damping may be responsible for the line shape of uranyl stretching vibrations.…”

Characterization of uranium tetrafluoride (UF4) with Raman spectroscopy

“…Ho et al reported a spectrum from a 'UF 4 ' sample provided by the International Atomic Energy Agency (λ ex = 785 nm) with prominent bands around 860 and 400 cm À1 that were attributed to UF 4 . [20] The spectrum most likely represented a combination of aging and decomposition products. The band located around 860 cm À1 was most likely because of a uranyl compound such as uranyl fluoride.…”

Nuclear forensic signatures and structural analysis of uranyl oxalate, its products of thermal decomposition and Fe impurity dopant

“…The process occurs by addition of oxalic acid to uranyl nitrate, forming an intermediate oxalate precipitate, which is calcined to uranium oxide (U 3 O 8 ) for eventual storage. Other intermediates exist, such as uranyl peroxide ([(UO 2 )(O 2 )(H 2 O) 2 ]•2H 2 O), which is produced following a similar processing route and has been extensively studied for its material properties [2][3][4][5][6]. Furthermore, some recent characterisations have been focused on the nuclear forensic implications of uranyl peroxides and its oxides [7].…”